It is known to prepare rigid polyurethane (PUR) and polyisocyanurate (PIR) foams by the reaction of a polyisocyanate, a polyol and a blowing agent in the presence of a catalyst. A wide variety of polyols have been used as one of the components in preparing rigid foams, including polyols made from scrap polyethylene terephthalate or from dimethyl terephthalate process residue.
The use of scrap polyethylene terephthalate (PET), also referred to in the art as recycled PET, for the preparation of rigid polyurethane foams is described, for example, in U.S. Pat. No. 4,439,550 and U.S. Pat. No. 4,439,551. These patents disclose that a mixture of aromatic polyols for use in preparing rigid foams can be prepared by transesterifying recycled PET with the reaction product of a residue from dibasic acid manufacture and an alkylene glycol. U.S. Pat. No. 4,469,824 describes the preparation of a mixture of liquid terephthalic ester polyols produced by reacting recycled polyethylene terephthalate with diethylene glycol and at least one more oxyalkylene glycol, and stripping out some of the ethylene glycol present. These polyols are useful as extenders in rigid polyurethane foams and as the sole polyol component in polyisocyanurate foams. A mixture of aromatic polyols prepared by transesterifying recycled polyethylene terephthalate with the reaction product of an aromatic carbonyl-containing compound and an alkylene glycol is described in U.S. Pat No. 4,506,090.
The use of by-products produced in the manufacture of dimethyl terephthalate (DMT) as the polyol component in polyisocyanurate foams is described, for example, in U.S. Pat. No. 4,411,949. In this patent a polyol mixture is obtained by transesterifying a by-product fraction from the manufacture of dimethyl terephthalate with a glycol. U.S. Pat. No. 4,346,229 discloses the product produced by reacting DMT process residue with dipropylene glycol or a mixture of glycols. In U.S. Pat. No. 4,444,918 a terephthalic ester waste stream from the manufacture of PET or DMT is transesterified with the reaction product of a residue from dibasic acid manufacture and an alkylene glycol to produce polyols for rigid foams. U.S. Pat. No. 4,444,920 relates to a mixture of aromatic polyols, suitable for use in rigid foams, prepared by reacting a DMT waste stream over a metal alkoxide catalyst and then transesterifying the product with a polyalkylene glycol.
Presently available polyols made from scrap PET or DMT process residue suffer from a variety of disadvantages such as the settling of solids from solution upon standing and lack of compatibility with the fluorocarbon blowing agents commonly used in the manufacture of rigid foams. Foams prepared from these polyols are sometimes deficient in compressive strength or in flame resistance or both.